Determinants of “P” wave location in narrow qrs tachycardia ?

Identifying the P wave is the key to decode any narrow QRS tachycardia . Though the the relationship to p and qrs is vita , many times it is not easy to relate them.More easily one may get a clue to the mechanism by analysing P wave timing .This is the basis of calling narrow qrs tachycardia as short RP and long RP.

Wonder . . . why the relation “P to R” became “R to P” here !

Since in the common narrow qrs tachycardias AVNRT/AVRT , atria activates the atria in a retrograde manner , we look for the relationship of qrs complex on subsequent P wave . Hence the interval between R to P become the focus.

The P wave location in narrow qrs tachycardia is primarily determined by the retrograde VA conduction and less on the antegrade AV conduction . Looking at the interval between R and P is a quick way of getting the VA conduction in the bed side.

Once we get an idea how the VA circuit conducts , we can narrow down the possibilities in Narrow qrs tachycardias !